pcie_bifurcation: Fetch bifurcation at a PCIe slot with hardcoded values

This will read a json config and return the bifurcation based on that.
It will read the configure file in a persistent file to see if it is
valid machine config and return the bifurcation information
accordingly.

For example,
If it is valid config, it will return 8x8 for PE1,3,4,6.

Tested:
Unit tests passed.

Physical Tests.

PE0 -> no bifurcation
PE1 -> x8x8

```
$ ipmitool raw 0x2e 0x32 0x79 0x2b 0x00 0x0f 0
 79 2b 00 0b 00

$ ipmitool raw 0x2e 0x32 0x79 0x2b 0x00 0x0f 1
 79 2b 00 0b 02 08 08
```

Change-Id: I44aefbfb26372f8bc0069343c8a6d07d3cf6f42d
Signed-off-by: Willy Tu <wltu@google.com>
diff --git a/handler.cpp b/handler.cpp
index 8ec7863..28408f2 100644
--- a/handler.cpp
+++ b/handler.cpp
@@ -599,5 +599,11 @@
     }
 }
 
+std::vector<uint8_t> Handler::pcieBifurcation(uint8_t index)
+{
+    return bifurcationHelper.get().getBifurcation(index).value_or(
+        std::vector<uint8_t>{});
+}
+
 } // namespace ipmi
 } // namespace google